EGR gas composition effects on ignition delays in diesel combustion

This paper presents the effects on ignition delays of a range of exhaust gas compositions recirculated in the intake air. The ignition delays were measured in a single-cylinder diesel engine introducing a variety of hydrocarbons, nitrogen oxides (NOx), and carbon monoxide (CO) into the intake gas, and changing the concentrations of these components. The experimental results show that the ignition delay decreases with the NOx addition, NO2 promotes the ignition more than NO, and this effect is more pronounced at higher intake gas temperatures. The ignition delay decreases with HC addition under NOx rich conditions while there is little effect under low NOx conditions, and the ignition delay changes with the kinds of hydrocarbons. The CO has little effect on the ignition delay. With the aid of chemical reaction analysis, the mechanisms of these changes are elucidated.